[PATCH] kprobe: fix resume execution on i386

[mirror_ubuntu-zesty-kernel.git] / arch / i386 / kernel / kprobes.c

/*
 *  Kernel Probes (KProbes)
 *  arch/i386/kernel/kprobes.c
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (C) IBM Corporation, 2002, 2004
 *
 * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
 *              Probes initial implementation ( includes contributions from
 *              Rusty Russell).
 * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
 *              interface to access function arguments.
 * 2005-May     Hien Nguyen <hien@us.ibm.com>, Jim Keniston
 *              <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
 *              <prasanna@in.ibm.com> added function-return probes.
 */

#include <linux/config.h>
#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/preempt.h>
#include <asm/cacheflush.h>
#include <asm/kdebug.h>
#include <asm/desc.h>
#include <asm/uaccess.h>

void jprobe_return_end(void);

DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);

/* insert a jmp code */
static __always_inline void set_jmp_op(void *from, void *to)
{
        struct __arch_jmp_op {
                char op;
                long raddr;
        } __attribute__((packed)) *jop;
        jop = (struct __arch_jmp_op *)from;
        jop->raddr = (long)(to) - ((long)(from) + 5);
        jop->op = RELATIVEJUMP_INSTRUCTION;
}

/*
 * returns non-zero if opcodes can be boosted.
 */
static __always_inline int can_boost(kprobe_opcode_t opcode)
{
        switch (opcode & 0xf0 ) {
        case 0x70:
                return 0; /* can't boost conditional jump */
        case 0x90:
                /* can't boost call and pushf */
                return opcode != 0x9a && opcode != 0x9c;
        case 0xc0:
                /* can't boost undefined opcodes and soft-interruptions */
                return (0xc1 < opcode && opcode < 0xc6) ||
                        (0xc7 < opcode && opcode < 0xcc) || opcode == 0xcf;
        case 0xd0:
                /* can boost AA* and XLAT */
                return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7);
        case 0xe0:
                /* can boost in/out and (may be) jmps */
                return (0xe3 < opcode && opcode != 0xe8);
        case 0xf0:
                /* clear and set flags can be boost */
                return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
        default:
                /* currently, can't boost 2 bytes opcodes */
                return opcode != 0x0f;
        }
}


/*
 * returns non-zero if opcode modifies the interrupt flag.
 */
static int __kprobes is_IF_modifier(kprobe_opcode_t opcode)
{
        switch (opcode) {
        case 0xfa:              /* cli */
        case 0xfb:              /* sti */
        case 0xcf:              /* iret/iretd */
        case 0x9d:              /* popf/popfd */
                return 1;
        }
        return 0;
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
        /* insn: must be on special executable page on i386. */
        p->ainsn.insn = get_insn_slot();
        if (!p->ainsn.insn)
                return -ENOMEM;

        memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
        p->opcode = *p->addr;
        if (can_boost(p->opcode)) {
                p->ainsn.boostable = 0;
        } else {
                p->ainsn.boostable = -1;
        }
        return 0;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        *p->addr = BREAKPOINT_INSTRUCTION;
        flush_icache_range((unsigned long) p->addr,
                           (unsigned long) p->addr + sizeof(kprobe_opcode_t));
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
        *p->addr = p->opcode;
        flush_icache_range((unsigned long) p->addr,
                           (unsigned long) p->addr + sizeof(kprobe_opcode_t));
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
        mutex_lock(&kprobe_mutex);
        free_insn_slot(p->ainsn.insn);
        mutex_unlock(&kprobe_mutex);
}

static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
        kcb->prev_kprobe.kp = kprobe_running();
        kcb->prev_kprobe.status = kcb->kprobe_status;
        kcb->prev_kprobe.old_eflags = kcb->kprobe_old_eflags;
        kcb->prev_kprobe.saved_eflags = kcb->kprobe_saved_eflags;
}

static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
        __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
        kcb->kprobe_status = kcb->prev_kprobe.status;
        kcb->kprobe_old_eflags = kcb->prev_kprobe.old_eflags;
        kcb->kprobe_saved_eflags = kcb->prev_kprobe.saved_eflags;
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                                struct kprobe_ctlblk *kcb)
{
        __get_cpu_var(current_kprobe) = p;
        kcb->kprobe_saved_eflags = kcb->kprobe_old_eflags
                = (regs->eflags & (TF_MASK | IF_MASK));
        if (is_IF_modifier(p->opcode))
                kcb->kprobe_saved_eflags &= ~IF_MASK;
}

static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
        regs->eflags |= TF_MASK;
        regs->eflags &= ~IF_MASK;
        /*single step inline if the instruction is an int3*/
        if (p->opcode == BREAKPOINT_INSTRUCTION)
                regs->eip = (unsigned long)p->addr;
        else
                regs->eip = (unsigned long)p->ainsn.insn;
}

/* Called with kretprobe_lock held */
void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
                                      struct pt_regs *regs)
{
        unsigned long *sara = (unsigned long *)&regs->esp;
        struct kretprobe_instance *ri;

        if ((ri = get_free_rp_inst(rp)) != NULL) {
                ri->rp = rp;
                ri->task = current;
                ri->ret_addr = (kprobe_opcode_t *) *sara;

                /* Replace the return addr with trampoline addr */
                *sara = (unsigned long) &kretprobe_trampoline;

                add_rp_inst(ri);
        } else {
                rp->nmissed++;
        }
}

/*
 * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 * remain disabled thorough out this function.
 */
static int __kprobes kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *p;
        int ret = 0;
        kprobe_opcode_t *addr;
        struct kprobe_ctlblk *kcb;
#ifdef CONFIG_PREEMPT
        unsigned pre_preempt_count = preempt_count();
#endif /* CONFIG_PREEMPT */

        addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t));

        /*
         * We don't want to be preempted for the entire
         * duration of kprobe processing
         */
        preempt_disable();
        kcb = get_kprobe_ctlblk();

        /* Check we're not actually recursing */
        if (kprobe_running()) {
                p = get_kprobe(addr);
                if (p) {
                        if (kcb->kprobe_status == KPROBE_HIT_SS &&
                                *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
                                regs->eflags &= ~TF_MASK;
                                regs->eflags |= kcb->kprobe_saved_eflags;
                                goto no_kprobe;
                        }
                        /* We have reentered the kprobe_handler(), since
                         * another probe was hit while within the handler.
                         * We here save the original kprobes variables and
                         * just single step on the instruction of the new probe
                         * without calling any user handlers.
                         */
                        save_previous_kprobe(kcb);
                        set_current_kprobe(p, regs, kcb);
                        kprobes_inc_nmissed_count(p);
                        prepare_singlestep(p, regs);
                        kcb->kprobe_status = KPROBE_REENTER;
                        return 1;
                } else {
                        if (*addr != BREAKPOINT_INSTRUCTION) {
                        /* The breakpoint instruction was removed by
                         * another cpu right after we hit, no further
                         * handling of this interrupt is appropriate
                         */
                                regs->eip -= sizeof(kprobe_opcode_t);
                                ret = 1;
                                goto no_kprobe;
                        }
                        p = __get_cpu_var(current_kprobe);
                        if (p->break_handler && p->break_handler(p, regs)) {
                                goto ss_probe;
                        }
                }
                goto no_kprobe;
        }

        p = get_kprobe(addr);
        if (!p) {
                if (*addr != BREAKPOINT_INSTRUCTION) {
                        /*
                         * The breakpoint instruction was removed right
                         * after we hit it.  Another cpu has removed
                         * either a probepoint or a debugger breakpoint
                         * at this address.  In either case, no further
                         * handling of this interrupt is appropriate.
                         * Back up over the (now missing) int3 and run
                         * the original instruction.
                         */
                        regs->eip -= sizeof(kprobe_opcode_t);
                        ret = 1;
                }
                /* Not one of ours: let kernel handle it */
                goto no_kprobe;
        }

        set_current_kprobe(p, regs, kcb);
        kcb->kprobe_status = KPROBE_HIT_ACTIVE;

        if (p->pre_handler && p->pre_handler(p, regs))
                /* handler has already set things up, so skip ss setup */
                return 1;

        if (p->ainsn.boostable == 1 &&
#ifdef CONFIG_PREEMPT
            !(pre_preempt_count) && /*
                                       * This enables booster when the direct
                                       * execution path aren't preempted.
                                       */
#endif /* CONFIG_PREEMPT */
            !p->post_handler && !p->break_handler ) {
                /* Boost up -- we can execute copied instructions directly */
                reset_current_kprobe();
                regs->eip = (unsigned long)p->ainsn.insn;
                preempt_enable_no_resched();
                return 1;
        }

ss_probe:
        prepare_singlestep(p, regs);
        kcb->kprobe_status = KPROBE_HIT_SS;
        return 1;

no_kprobe:
        preempt_enable_no_resched();
        return ret;
}

/*
 * For function-return probes, init_kprobes() establishes a probepoint
 * here. When a retprobed function returns, this probe is hit and
 * trampoline_probe_handler() runs, calling the kretprobe's handler.
 */
 void __kprobes kretprobe_trampoline_holder(void)
 {
        asm volatile ( ".global kretprobe_trampoline\n"
                        "kretprobe_trampoline: \n"
                        "       pushf\n"
                        /* skip cs, eip, orig_eax, es, ds */
                        "       subl $20, %esp\n"
                        "       pushl %eax\n"
                        "       pushl %ebp\n"
                        "       pushl %edi\n"
                        "       pushl %esi\n"
                        "       pushl %edx\n"
                        "       pushl %ecx\n"
                        "       pushl %ebx\n"
                        "       movl %esp, %eax\n"
                        "       call trampoline_handler\n"
                        /* move eflags to cs */
                        "       movl 48(%esp), %edx\n"
                        "       movl %edx, 44(%esp)\n"
                        /* save true return address on eflags */
                        "       movl %eax, 48(%esp)\n"
                        "       popl %ebx\n"
                        "       popl %ecx\n"
                        "       popl %edx\n"
                        "       popl %esi\n"
                        "       popl %edi\n"
                        "       popl %ebp\n"
                        "       popl %eax\n"
                        /* skip eip, orig_eax, es, ds */
                        "       addl $16, %esp\n"
                        "       popf\n"
                        "       ret\n");
}

/*
 * Called from kretprobe_trampoline
 */
fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)
{
        struct kretprobe_instance *ri = NULL;
        struct hlist_head *head;
        struct hlist_node *node, *tmp;
        unsigned long flags, orig_ret_address = 0;
        unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;

        spin_lock_irqsave(&kretprobe_lock, flags);
        head = kretprobe_inst_table_head(current);

        /*
         * It is possible to have multiple instances associated with a given
         * task either because an multiple functions in the call path
         * have a return probe installed on them, and/or more then one return
         * return probe was registered for a target function.
         *
         * We can handle this because:
         *     - instances are always inserted at the head of the list
         *     - when multiple return probes are registered for the same
         *       function, the first instance's ret_addr will point to the
         *       real return address, and all the rest will point to
         *       kretprobe_trampoline
         */
        hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
                if (ri->task != current)
                        /* another task is sharing our hash bucket */
                        continue;

                if (ri->rp && ri->rp->handler){
                        __get_cpu_var(current_kprobe) = &ri->rp->kp;
                        ri->rp->handler(ri, regs);
                        __get_cpu_var(current_kprobe) = NULL;
                }

                orig_ret_address = (unsigned long)ri->ret_addr;
                recycle_rp_inst(ri);

                if (orig_ret_address != trampoline_address)
                        /*
                         * This is the real return address. Any other
                         * instances associated with this task are for
                         * other calls deeper on the call stack
                         */
                        break;
        }

        BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));

        spin_unlock_irqrestore(&kretprobe_lock, flags);

        return (void*)orig_ret_address;
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "int 3"
 * instruction.  To avoid the SMP problems that can occur when we
 * temporarily put back the original opcode to single-step, we
 * single-stepped a copy of the instruction.  The address of this
 * copy is p->ainsn.insn.
 *
 * This function prepares to return from the post-single-step
 * interrupt.  We have to fix up the stack as follows:
 *
 * 0) Except in the case of absolute or indirect jump or call instructions,
 * the new eip is relative to the copied instruction.  We need to make
 * it relative to the original instruction.
 *
 * 1) If the single-stepped instruction was pushfl, then the TF and IF
 * flags are set in the just-pushed eflags, and may need to be cleared.
 *
 * 2) If the single-stepped instruction was a call, the return address
 * that is atop the stack is the address following the copied instruction.
 * We need to make it the address following the original instruction.
 *
 * This function also checks instruction size for preparing direct execution.
 */
static void __kprobes resume_execution(struct kprobe *p,
                struct pt_regs *regs, struct kprobe_ctlblk *kcb)
{
        unsigned long *tos = (unsigned long *)&regs->esp;
        unsigned long copy_eip = (unsigned long)p->ainsn.insn;
        unsigned long orig_eip = (unsigned long)p->addr;

        regs->eflags &= ~TF_MASK;
        switch (p->ainsn.insn[0]) {
        case 0x9c:              /* pushfl */
                *tos &= ~(TF_MASK | IF_MASK);
                *tos |= kcb->kprobe_old_eflags;
                break;
        case 0xc2:              /* iret/ret/lret */
        case 0xc3:
        case 0xca:
        case 0xcb:
        case 0xcf:
        case 0xea:              /* jmp absolute -- eip is correct */
                /* eip is already adjusted, no more changes required */
                p->ainsn.boostable = 1;
                goto no_change;
        case 0xe8:              /* call relative - Fix return addr */
                *tos = orig_eip + (*tos - copy_eip);
                break;
        case 0x9a:              /* call absolute -- same as call absolute, indirect */
                *tos = orig_eip + (*tos - copy_eip);
                goto no_change;
        case 0xff:
                if ((p->ainsn.insn[1] & 0x30) == 0x10) {
                        /*
                         * call absolute, indirect
                         * Fix return addr; eip is correct.
                         * But this is not boostable
                         */
                        *tos = orig_eip + (*tos - copy_eip);
                        goto no_change;
                } else if (((p->ainsn.insn[1] & 0x31) == 0x20) ||       /* jmp near, absolute indirect */
                           ((p->ainsn.insn[1] & 0x31) == 0x21)) {       /* jmp far, absolute indirect */
                        /* eip is correct. And this is boostable */
                        p->ainsn.boostable = 1;
                        goto no_change;
                }
        default:
                break;
        }

        if (p->ainsn.boostable == 0) {
                if ((regs->eip > copy_eip) &&
                    (regs->eip - copy_eip) + 5 < MAX_INSN_SIZE) {
                        /*
                         * These instructions can be executed directly if it
                         * jumps back to correct address.
                         */
                        set_jmp_op((void *)regs->eip,
                                   (void *)orig_eip + (regs->eip - copy_eip));
                        p->ainsn.boostable = 1;
                } else {
                        p->ainsn.boostable = -1;
                }
        }

        regs->eip = orig_eip + (regs->eip - copy_eip);

no_change:
        return;
}

/*
 * Interrupts are disabled on entry as trap1 is an interrupt gate and they
 * remain disabled thoroughout this function.
 */
static int __kprobes post_kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        if (!cur)
                return 0;

        if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
                kcb->kprobe_status = KPROBE_HIT_SSDONE;
                cur->post_handler(cur, regs, 0);
        }

        resume_execution(cur, regs, kcb);
        regs->eflags |= kcb->kprobe_saved_eflags;

        /*Restore back the original saved kprobes variables and continue. */
        if (kcb->kprobe_status == KPROBE_REENTER) {
                restore_previous_kprobe(kcb);
                goto out;
        }
        reset_current_kprobe();
out:
        preempt_enable_no_resched();

        /*
         * if somebody else is singlestepping across a probe point, eflags
         * will have TF set, in which case, continue the remaining processing
         * of do_debug, as if this is not a probe hit.
         */
        if (regs->eflags & TF_MASK)
                return 0;

        return 1;
}

static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        switch(kcb->kprobe_status) {
        case KPROBE_HIT_SS:
        case KPROBE_REENTER:
                /*
                 * We are here because the instruction being single
                 * stepped caused a page fault. We reset the current
                 * kprobe and the eip points back to the probe address
                 * and allow the page fault handler to continue as a
                 * normal page fault.
                 */
                regs->eip = (unsigned long)cur->addr;
                regs->eflags |= kcb->kprobe_old_eflags;
                if (kcb->kprobe_status == KPROBE_REENTER)
                        restore_previous_kprobe(kcb);
                else
                        reset_current_kprobe();
                preempt_enable_no_resched();
                break;
        case KPROBE_HIT_ACTIVE:
        case KPROBE_HIT_SSDONE:
                /*
                 * We increment the nmissed count for accounting,
                 * we can also use npre/npostfault count for accouting
                 * these specific fault cases.
                 */
                kprobes_inc_nmissed_count(cur);

                /*
                 * We come here because instructions in the pre/post
                 * handler caused the page_fault, this could happen
                 * if handler tries to access user space by
                 * copy_from_user(), get_user() etc. Let the
                 * user-specified handler try to fix it first.
                 */
                if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
                        return 1;

                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.
                 */
                if (fixup_exception(regs))
                        return 1;

                /*
                 * fixup_exception() could not handle it,
                 * Let do_page_fault() fix it.
                 */
                break;
        default:
                break;
        }
        return 0;
}

/*
 * Wrapper routine to for handling exceptions.
 */
int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                                       unsigned long val, void *data)
{
        struct die_args *args = (struct die_args *)data;
        int ret = NOTIFY_DONE;

        if (args->regs && user_mode(args->regs))
                return ret;

        switch (val) {
        case DIE_INT3:
                if (kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
        case DIE_DEBUG:
                if (post_kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
        case DIE_GPF:
        case DIE_PAGE_FAULT:
                /* kprobe_running() needs smp_processor_id() */
                preempt_disable();
                if (kprobe_running() &&
                    kprobe_fault_handler(args->regs, args->trapnr))
                        ret = NOTIFY_STOP;
                preempt_enable();
                break;
        default:
                break;
        }
        return ret;
}

int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct jprobe *jp = container_of(p, struct jprobe, kp);
        unsigned long addr;
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        kcb->jprobe_saved_regs = *regs;
        kcb->jprobe_saved_esp = &regs->esp;
        addr = (unsigned long)(kcb->jprobe_saved_esp);

        /*
         * TBD: As Linus pointed out, gcc assumes that the callee
         * owns the argument space and could overwrite it, e.g.
         * tailcall optimization. So, to be absolutely safe
         * we also save and restore enough stack bytes to cover
         * the argument area.
         */
        memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr,
                        MIN_STACK_SIZE(addr));
        regs->eflags &= ~IF_MASK;
        regs->eip = (unsigned long)(jp->entry);
        return 1;
}

void __kprobes jprobe_return(void)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        asm volatile ("       xchgl   %%ebx,%%esp     \n"
                      "       int3                      \n"
                      "       .globl jprobe_return_end  \n"
                      "       jprobe_return_end:        \n"
                      "       nop                       \n"::"b"
                      (kcb->jprobe_saved_esp):"memory");
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        u8 *addr = (u8 *) (regs->eip - 1);
        unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_esp);
        struct jprobe *jp = container_of(p, struct jprobe, kp);

        if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
                if (&regs->esp != kcb->jprobe_saved_esp) {
                        struct pt_regs *saved_regs =
                            container_of(kcb->jprobe_saved_esp,
                                            struct pt_regs, esp);
                        printk("current esp %p does not match saved esp %p\n",
                               &regs->esp, kcb->jprobe_saved_esp);
                        printk("Saved registers for jprobe %p\n", jp);
                        show_registers(saved_regs);
                        printk("Current registers\n");
                        show_registers(regs);
                        BUG();
                }
                *regs = kcb->jprobe_saved_regs;
                memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
                       MIN_STACK_SIZE(stack_addr));
                preempt_enable_no_resched();
                return 1;
        }
        return 0;
}

int __init arch_init_kprobes(void)
{
        return 0;
}